Impacts of large projects on the sediment dynamics and evolution of the Hengsha Shoal in the Yangtze Delta

Response of Shallow Gas‐Charged Holocene Deposits in the Yangtze Delta to Meter‐Scale Erosion Induced by Diminished Sediment Supply: Increasing Greenhouse Gas Emissions

“…The mean grain size of the core sediments in the southern area is typically ∼7Φ (Liu, Saito, et al., 2010; Xu et al., 2013; Zhan et al., 2011), while it varies between 4 and 5 Φ in the uppermost ∼10 m of the sediments in the north (Zhao et al., 2018). Similarly, the mean grain sizes of the surficial sediments in the south and north are generally 6–7 Φ and 4–5 Φ, respectively (Wang, 2011). The difference in the grain size composition is responsible for the difference in the erodibility of the bed sediments.…”

“…From the perspective of stratigraphy and lithology, shallow gas originates from muddy facies corresponding to Holocene TST and HST sediments. Sediment cores from different regions of the subaqueous delta indicate that the total organic carbon content in sediments throughout the Holocene from the TST to the HST is generally 0.5% or higher (Wang, 2011; Wang et al., 2012; Zhan et al., 2011; Zhang, Jin, et al., 2015; Zhang et al., 2011), which is above the threshold value for gas generation (Rice & Claypool, 1981). Although the masking effect hinders the identification of deeper gas horizons, most Holocene sediments below the gas front are likely gas‐charged.…”